Fix migration collection

apps/collection/migrations/0012_auto_20190923_1340.py

@@ -0,0 +1,19 @@
+# Generated by Django 2.2.4 on 2019-09-23 13:40
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('collection', '0011_auto_20190920_1059'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='guide',
+            name='parent',
+            field=models.ForeignKey(blank=True, default=None, null=True, on_delete=django.db.models.deletion.CASCADE, to='collection.Guide', verbose_name='parent'),
+        ),
+    ]